In general, closure fastening devices for use in connection with plastic bags and the like are known. Furthermore, manufacturing methods for closure fastening devices made of plastic material are generally well-known.
In operation, a closure fastening device for use in connection with a flexible container should be relatively easy to open from the outside, but relatively difficult to open from the inside. Generally, such a container can be used with its interior either under relatively high pressure or under relatively low pressure. The closure fastening device should provide a satisfactory seal for either condition.
Preferably, the closure fastening device should be suitable for economical manufacturing and should be relatively simple in design. In addition, the design should provide for variations in order to meet different needs. For example, it may be desirable to have a closure fastening device which is relatively difficult to open both from the inside and the outside. In general, the closure fastening device, however, should always be relatively easy to close.
In addition, when the closure fastening device is employed with a container, the container may be made from a thermoplastic material and the closure device and sidewalls of the container can be made integrally by extrusion as a unitary piece or can be made as separate components which are subsequently permanently connected together.
One prior art fastening device is disclosed in Thomas U.S. Pat. No. 3,535,746 comprising a generally omega-shaped bag fastener having extended legs and two outwardly curved arm portions. The fastener when placed about the neck of a bag is locked in place by twisting the legs into an intertwined engaged position. The fastener is made from a flexible resilient thermoplastic material such as polypropylene. However, the fastener of the '746 patent is not employed with a complementary fastener element.
Another prior art fastening device is disclosed by Kamp in U.S. Pat. No. 4,212,337. This device comprises a first U-shaped channel element including hook portions facing away from each other and a second U-shaped channel element including hook portions facing towards each other. The channel elements interlock by pressing the first channel element into the second channel element so that the hook portions engage each other at predetermined contact surfaces.
It should be appreciated that conventional thermoplastic interlocking closure fastening devices are made of deformable materials so as to employ the bending properties of the materials which form the bottom, leg, and hook portions, hereinafter referred to collectively as the "profile portions", of each closure element to occlude the elements to each other, and alternatively, to allow the elements to be separated as during their deocclusion. Thus, manipulation of such fastening devices requires the use of relatively soft, resilient resins since the closure elements have to be flexible to occlude or de-occlude.
One of the latest developments of plastic containers is a bag which can be used as a food storage container in a refrigerated or frozen condition as well as for heating and/or cooking food such as by placing the bag in hot water or in a microwave oven. When used in a microwave oven, it is not unusual for such bags to encounter temperatures of 260.degree. F. to 300.degree. F., for example, such as when cooking meats. Even during the boiling of foods, such as in a metal pot, temperatures higher than 212.degree. F. are sometimes obtained above the water level such as near the rim of the pot necessitating better temperature resistance to softening or melting of the plastic bag than can be provided by the frequently used polyethylene resins. In order to overcome such problems at elevated temperatures, it is known that higher melting point resins may be employed which generally have higher stiffness moduli and also therefore resist softening or melting. However, when such higher stiffness moduli resins are employed as the materials of construction for the closure device, the closure device resists bending and deflection, which are the most frequently used means of occlusion and de-occlusion of interlocking closure devices made from flexible resins such as polyethylene.
Therefore, it would be highly desirable to obtain an interlocking closure device having relative ease of occlusion and de-occlusion, wherein the interlocking closure device, if so desired, is resistant to elevated temperature, the closure device may be manufactured with ample tolerance latitude, and wherein the operation of the closure elements is truly mechanical and not dependent upon the deflection characterized of the closure elements.